Optimizing FPGAs for power: A full-frontal attack

Editor's Note: I am delighted to have the opportunity to present the following piece from the fourth quarter edition of the Xcell Journal, with the kind permission of Xilinx Inc.

This piece is a hands-on how to optimize FPGA designs for low power operation. This is a universal topic but, of course, it is really important for wireless and mobile military and aerospace applications that run on battery power. Such applications go from planes, to drones to frontline soldier communication equipment.

The article is a rundown of low-power design techniques for the latest families of 7 series FPGAs at each stage of the development cycle.

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Power has become a primary factor in the ever-important search for the “perfect” FPGA for a given design. Power management is critical in most applications. Some standards specify maximum power per card or per system. As such, designers must consider power much earlier in the design flow than ever before—often starting with the selection of an FPGA.

Reducing the power consumption of the FPGA simplifies the board design by lowering the supply rails, simplifying power supply design and thermal management, and easing the requirements on the power distribution planes. Low power also contributes to longer battery life and higher reliability (cooler-running systems last longer) of the system.

POWER CHALLENGESWith each generation of process technology, transistors are becoming smaller and smaller in accordance with Moore’s Law. This phenomenon has the unfortunate side effect of incurring more leakage within each transistor, which leads to higher static power consumption—that is, the amount of current an FPGA draws when not operating. Increased FPGA performance drives the clock rate higher, which leads to higher levels of dynamic power. Where static power is driven by transistor leakage current, dynamic power is based on the switching frequency in the programmable logic and I/Os. Exacerbating both types of power consumption, FPGAs are growing in capacity with each product generation. More logic means more leakage and more transistors operating at higher speeds per device.

Because of these issues, designers must be more aware of their power supply and thermal-management issues earlier in their design cycles. Slapping a heat sink over a device may not adequately resolve these issues. Instead, designers must look for opportunities to reduce the logic in the design.

Let’s take a look at some guidelines that will help you understand what type of action to take at various points in the design cycle to reduce the power consumption of an FPGA design. Clearly, having a thorough understanding of these issues early in the design process will yield the greatest reward.

Figure 1 illustrates different points in the design cycle, from FPGA selection through low-power design techniques.

This is an excellent overview of the methods that can be used to improve power characteristics. Going forward this will be a more and more important aspect of design and will need to be tightly integrated with capacity and timing constraints in the design software. Just don't make me deal with another set of design constraints, PLEASE. Isn't it about time to find another way to meet design objectives? Any ides out there?